This invention relates generally to storage and dispensing systems for the selective dispensing of gaseous compounds, in particular hazardous hydride and halide gases, from a storage container in which the gaseous compounds are held in sorptive relationship to a solid sorbent medium, and are desorptively released from the sorbent medium in the dispensing operation.
The semiconductor manufacturing industry uses a number of hazardous specialty gases for doping, etching and thin-film deposition. For example, phosphine (PH.sub.3) and arsine (AsH.sub.3) are needed for numerous semiconductor fabrication processes, though their use poses significant safety and environmental challenges due to their high toxicity and pyrophoricity (i.e., spontaneous inflammability in air). The storage and transport of highly toxic or pyrophoric materials as compressed or liquefied gases in metal cylinders is often unacceptable because of the possibility of developing a leak or catastrophic rupture of the container which could lead to injuries or death. It would be preferable to have a reliable source of these gases wherein the gases are maintained at or below atmospheric pressure during shipping and storage. Also, since many semiconductor processes using specialty gases are operated below ambient pressure, positive gauge pressures of these gases may not be needed, even when in use.
In order to mitigate some of these safety issues, on-site electrochemical generation of such gases has been described. See, e.g., U.S. Pat. Nos. 4,178,224, 5,158,656, 5,425,857 and 5,474,659. Because of difficulties in the on-site synthesis of these gases, a better technique has been developed where the gas is physisorbed or chemisorbed on a support, thereby reducing the vapor pressure of the gas to render it safer. For example, U.S. Pat. No. 5,518,528 to Tom et al. discloses such a process wherein PH.sub.3 and AsH.sub.3 are adsorbed on physical sorbent and chemisorbent materials, such as strongly basic adsorbents dispersed in, but not covalently bonded to a support. The strong bases presumably react at the surface with the weakly acidic protons on the hydride gas molecules.
It would be more desirable to have a system where the hazardous specialty gas could be reversibly immobilized by undergoing a chemical reaction with the bulk of the solid sorbent. This approach has the potential for higher sorption capacities compared to the surface adsorption and chemisorption approaches of the prior art. The ability to tune the chemical reactivity of the sorbent also provides far greater control over the equilibrium pressure of the hazardous gas over the solid.
All references cited herein are incorporated herein by reference in their entireties.